The effect of changes in intestinal tissue PO2 on blood flow will be investigated during resting and glucose absorption states. The purpose of these studies is to determine if the status of tissue PO2 is involved in the hypermia associated with intestinal absorption. All studies will be done on exteriorized loops of small intestine in anesthetized rats. Tissue PO2 will be measured with oxygen sensitive microelectrodes and tissue PO2's will be raised or lowered by adjustments of PO2 in fluid bathing the tissue. The normal PO2 event is a decrease in mucosal PO2 from 14-15mmHg at rest to 7-8 mmHg during absorption. If an increase in tissue PO2 during absorption to a normal resting level lessens the hypermia associated with absorption, a direct or indirect effect of oxygen is implicated. Furthermore, if at rest (no absorption) a decrease in mucosal PO2 to levels comparable to that during absorption should cause hypermia, this behavior would also implicate a dependency of the absorptive hyperemia mechanism on tissue PO2. However, if both tests fail to produce proposed responses, it is likely that agents other than oxygen are involved in the absorptive hyperemia mechanism.